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Macrobials in biocontrol beginner’s guide: Types, and how to use

Theme: Basics of biocontrol

Theme: Biocontrol agents

Overview

What are macrobials in biocontrol?

Macrobials, or invertebrate biocontrol agents (IBCAs), are living organisms that can control crop pests. They are small animals, such as beneficial insects, nematodes, and mites. They control pests by direct consumption or infection.

Macrobials are used in biological control, as are biopesticides (microbials, semiochemicals and natural substances).

Some examples of commercialized macrobial products are:

  • Spical Ulti-Mite (Spical Ulti-Mite DE, GB, PE, CA, US): predatory mites that control spider mites.
  • Trichosafe (DE): parasitoid wasps that control the European corn borer.
  • Bio Atheta (US, CA): rove beetles that control thrips, fungus gnats and other pests living in the soil.
  • Nematop (HU, DE, ES): nematodes that control the vine weevil.

Types of macrobials in biocontrol

We can separate macrobials into three groups based on their characteristics and how they work:

  • Predators: insects or mites that kill and feed on pests.
  • Parasitoids: insects that live and feed inside or on pests, eventually killing them.
  • Entomopathogenic nematodes: parasitic nematodes that infect and kill insect pests. 
three images showing macrobail types. They are a predatory spined soldier bug eating a caterpillar, a parasitoid wasp laying eggs in an armyworm egg and entomopathogenic nematodes bursting from an infected insect body
From left to right: a predatory nymph of a spined soldier bug (Podisus maculiventris) eating a caterpillar pest; a parasitoid wasp (Trichogramma dendrolimi) parasitizing an armyworm egg; entomopathogenic nematodes (Heterorhabditis bacteriophora) bursting from an infected insect body. Credit: Russ Ottens via Bugwood.org; Victor Fursov via Wikipedia commons; Peggy Greb via Bugwood.org.

Predator macrobials in biocontrol

Macrobial predators are invertebrates that kill and eat pests. A predator can hunt for its prey, the pest, and locate it on the crop, or wait for the prey to come near it. Once the predator finds the pest, it kills and eats it.

Sometimes both immature and adult stages of predators feed on prey, for example, ladybirds; however, sometimes only one of the life stages is predatory, such as lacewings that only predate as larvae.

2 images of macrobial in biocontrol. Left: Immature life stage ladybird. Right: Fully-grown ladybird eating a pest.
Immature life stage (left) and adult life stage (right) of a ladybird. Credit: CABI (left) and Gilles San Martin via Flickr CC BY-SA 2.0 (right)

Predators include both mites and insects.

Predatory mites

These predators are from the same family as spiders. They eat other mites and insects, such as thrips, whiteflies, and scale insects.

All life stages of predatory mites feed on pests.

  • The predatory mite Amblyseius swirksii is one of the most successful macrobials on the market. It is used against major greenhouse pests like thrips, whiteflies, and mites.
  • Spical Ulti-Mite (DE, GB, PE, CA, US) is a product that contains the predatory mite Neoseiulus californicus. These predators feed on various species of spider mites. They pierce their prey and suck out their content, leaving an empty skin.

Predatory insects

Predatory insects feed on other insects and include, amongst others, lacewings, ladybirds and predatory beetles. Some predators are active hunters. They use various tactics to eat their prey. For instance, some predators, like ladybirds, chew on their prey. Some suck the content of their prey.

  • Adalia bipunctata (HU) is a predator ladybird. Both larvae and adult stages feed on aphids and other soft-bodied insects.  
  • The commercialized product, Bio Atheta (US, CA) contains adults of the rove beetle Dalotia coriaria. These beetles are predators that eat thrips, fungus gnats and other soil-dwelling insects.
  • Micromus (CA) contains a predatory bug, the brown lacewing (Micromus variegatus). This predator eats sucking insect pests such as aphids, whiteflies, and mealybugs.
A macrobial predatory insect on a leaf infested with whitefly nymphs
A predatory insect, the insidious flower bug (Orius insidiosus), feeding on whitefly nymphs. Credit: Jack Dykinga via Wikipedia commons.

Parasitoid macrobials in biocontrol

Parasitoids are insects that parasitize other arthropods, mainly insects. They limit the growth of their host, the pest, and eventually cause their death. A parasitoid lays eggs on or inside the host. The emergent larvae feed on the host, which weakens it. Eventually, the host dies. This makes parasitoids different from predators, which directly kill their host.

Insect parasitoids are mostly wasps and flies. Parasitoids can locate their host with various cues like smell or vibrations. They can attack all life stages of arthropods, but one parasitoid species is usually specific to one life stage.

  • For example, Trichosafe (DE) contains individuals of the parasitoid wasp, Trichogramma brassicae for control of the European corn borer (Ostrinia nubilalis). The parasitoids lay eggs inside the pest’s eggs, stopping their development and, later, causing them to die.
  • Aphidius matricariae (CA) is a parasitoid wasp of the Green peach aphid and the Cannabis aphid. The parasitoid lays its eggs in the juvenile or adult pest. The eggs later become larvae that eat the pest’s organs, eventually killing it.
A macrobial parasitoid (Encarsia noyesi) called a giant whitefly
A parasitoid (Encarsia noyesi) next to one of its hosts, a whitefly nymph. Credit: Jesse Rorabaugh via iNaturalist.

Entomopathogenic nematode macrobials in biocontrol

Entomopathogenic (insect-killing) nematodes (EPNs) are beneficial nematodes. They are small worms that infect and kill insects. They are often used to control caterpillars of insects that live in or near the soil, but they are also effective against pests that feed on leaves.

Nematodes form a special (‘symbiotic’) relationship with some bacteria. These bacteria live inside the nematodes but are not harmful to them. However, these bacteria are deadly to insects.

When nematodes come into contact with their host, they enter its body. Once inside, the nematodes release these bacteria, causing an infection inside the pest. The nematodes reproduce in the insect’s body and are released once it dies due to the infection. Released nematodes can infect more individuals.

Entomopathogenic nematodes macrobial as seen under the microscope
A microscopic view of juvenile entomopathogenic nematodes (Steinernema scapterisci). Credit: David Cappaert via Bugwood.org

  • For example, Steinernema-System (MA, PT, DE, ES, CR, GB, FR, CA, US) is a product that contains the nematode Steinernema feltiae. It targets soil-dwelling larvae of some pests, such as the fungus gnat and leaf miners.
  • The product Nematop (HU, DE, ES) contains nematodes of Heterorhabditis bacteriophora that control the vine weevil (Otiorhynchus sulcatus). Nematodes can kill both larvae and pupae of the vine weevil.

How different macrobials types work: modes of action

First, macrobials must find their host or prey. We distinguish two main behaviours:

  • Hunters/cruisers: these macrobials stalk and actively pursue their prey to eat or infect them. This is the case for predators like hoverflies and ladybirds. These macrobials usually use cues to find their prey, for example, olfactory (smell) or visual cues. Some macrobials, like, parasitoids, can use vibrations to locate their host.
  • Ambushers: these macrobials are less active and wait for their mobile prey to approach before attacking them. Some nematodes wait to ambush passing prey.
An adult predator macrobial biocontrol, Chrysoperla carnea
The green lacewing (Chrysoperla carnea), a predator that hunts its prey. Credit: Donald Hobern via Flickr CC BY-SA 2.0

Once macrobials find their host or prey, they can kill them in two ways:

  • Infection: macrobials infect their host, which dies later. Nematodes are the only macrobials that kill their prey by infecting them (using their bacteria).
  • Consumption: macrobials eat their prey, leading to their death. This is the case for predators and parasitoids. Predators eat their prey immediately, whereas parasitoids first lay eggs inside or on their prey. It is only when eggs hatch that the larvae slowly consume the host, eventually killing it.

How to apply different types of macrobials in biocontrol

Applying predator and parasitoid macrobials

Predators and parasitoids are usually released directly into the field. This means there is no need for additional equipment. They can be applied in their immature, non-predatory stage (as eggs, for example) or predatory stage. Immature macrobials still need to develop to be active and to start controlling pests. On the other hand, macrobials that are already predatory when purchased can control the pest immediately.

There are many ways to release predators and parasitoids into the field. Some common application methods are:

  • Slow-release/breeder sachets: these sachets contain predators but also some food so they can feed and reproduce. You can hang sachets on the crop plant, and predators are released gradually over several weeks. Example: Spical Ulti-Mite (DE, GB, PE, CA, US)
  • Cards: cards are especially common for Trichogramma parasitoids. The parasitoid eggs are glued onto the card, and the adults emerge later, ready to parasitize the pest. Cards are hung or stapled to plants.
  • Bottles: some predators simply come in a bottle. You can release the macrobials into the field by emptying the container on the crop.
  • Bags: macrobials can come in bags that have holes. You can hang the bags on the plants, and the predators or parasitoids can escape through the holes.
A farmer holding cards with macrobial Trichogramma eggs glued on it
Trichogramma eggs glued onto cards ready to be applied in the field. Copyright CABI

Applying entomopathogenic nematode macrobials

The application of nematodes differs from the application of predators and parasitoids. Nematodes are mixed with water first and then applied in the field.

Application methods for nematodes are:

  • Spraying: as nematodes are small organisms, they can be applied on the soil or foliage with standard sprayers. You need to adapt their sprayers to avoid clogging the spray equipment or killing the nematodes, for example, by removing filters, reducing spray pressure, etc.
  • Drenching: the mixture of nematodes and water can be poured directly on the soil.
  • Drip irrigation: nematodes can also be mixed with water in the field irrigation system. The filters must be appropriate as well to avoid clogging.

It is also important to adopt practices that ensure macrobials can survive and thrive in the environment. Thriving macrobials can reproduce and control pests for even longer. Some of these practices are:

  • Avoid spraying chemical pesticides where macrobials are introduced. Many chemical pesticides are broad-spectrum and can kill pests but also beneficial organisms like macrobials.
  • Provide alternative food sources by planting strips of flowering plants and cover crops for instance. You can also buy some products that provide other food sources when the prey numbers are low. For example, Entofood is an alternative food for the predatory bug Macrolophus pygmaeus.
  • Provide shelter: hedgerows, for example, are a shelter for many beneficial insects. Conserving hedgerows can help macrobials survive.

To learn more about how to use bioprotection products, read our ‘How to use bioprotection’ blog

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